Trimmer potentiometer with end terminals



' 1966 "r. M. PLACE, JR 3,

TRIMMER POTENTIOMETER WITH END TERMINALS Filed Oct. 22, 1962 IN V EN TOR.

THOMAS M. PLACE, JR.

ATTORNEY United States Patent i 3,227,987 TRIMMER POTENTIOMETER WITH END TERMINALS Thomas M. Place, .lr., Costa Mesa, Califi, assignor to Beckman Instruments, Inc., a corporation of California Filed Oct. 22, 1962, Ser. No. 232,002 2 Claims. (Cl. 338-312) This invention relates to a rigid terminal structure for resistance elements and, more particularly, to a rigid terminal structure for miniature resistance elements such as rectilinear trimmer potentiometers.

The present state of the art relating to rectilinear trimmer poteniometers is highly developed as exemplified by the co-pending application of James F. Gordon, Serial No. 584,008, entitled Potentiometer and Method of Manufacturing Same, filed May 10, 1956; the co-pending application of Jack E. Langenbach et al., Serial No. 166,054, and entitled Improved Variable Resistor, filed January 15, 1962; and the co-pending application of William J. H. Thoele, Serial No. 166,199, entitled Variable Resistance Dev-ice, filed January 15, 1962. Each of the foregoing applications are assigned to Beckman Instruments, Inc., assignee of the present invention.

It is the primary object of this invention to provide an improved rigid contact structure for resistance elements and in particular miniature variable resistance devices such as are described in the above-identified applications.

Conventional terminals for trimmer potentiometers comprise flexible insulated wires which extend through a hole or channel provided in the potentiometer body or frame. Electrical voltage breakdown or leakage between the terminal wires, or the terminal wires and a metallic potentiometer housing is limited by the insulation upon the flexible terminal wires. However, when design, space, or mounting consideration dictate that the electrical termination means comprise solderable rigid lugs, it is necessary to substitute relatively large rigid wires for the flexible insulated wires to attain a desirable degree or rigidity within the available space. This consideration, in turn, necessitates the use of a single strand bare conductor of larger diameter than is necessary when flexible conductors are employed. The use of larger wires within a given space increases the electrical leakage between the uninsulated conductors and increases the possibility of electrical breakdown to the potentiometer housing or to associated circuit components.

It is therefore another object of this invention to provide a rectilinear trimmer potentiometer having rigid so'lderable terminals protruding from the potentiometer which is not subject to significant electrical leakage or vulnerable to voltage breakdown.

Another object of the present invention is to provide a rigid terminal structure for resistance elements having substantial mechanical strength and resistance to heat so as to be particularly adapted for solderably attaching thereto lead wires from the associated circuitry.

Other and further objects, features and advantages of the invention will become apparent as the description proceeds.

Briefly, in accordance with a preferred form of the present invention, there is provided a rectilinear trimmer potentiometer having a support member upon which is mounted a resistance element and conductor element. Within the base of the support member are formed longitudinal grooves which respectively terminate at openings extending upward through the support member adjacent the resistance element and conductor element. Single strand bare conductors each having a broad 3,227,987 Patented Jan. 4, 1966 ice fiat head formed integral with one end thereof are passed through respective ones of said openings and said grooves with said flat head being retained against the top surface of said support member in electrical contact with the resistance element or conductor element. A sealing compound such as a low melting glass head is then fired around the wire within the opening so as to seal the wire to the support member.

Resistance elements constructed in the manner just described provide a rigid contact rigid termination through the end of the housing having substantial mechanical strength and heat resistance so that leads from other components can be readily soldered thereto without breakage of the terminal element. Moreover, the structure described provides a very high resistance leakage path between each of the conductors and the potentiometer housing and other circuit elements. The resultant unit therefore has insignificant electrical leakage and is not vulnerable to voltage breakdown.

A more thorough understanding of the invention may be obtained by a study of the following detailed description taken in connection with the accompanying drawings in which:

FIG. 1 illustrates a longitudinal cross-section of a trimmer potentiometer constructed according to the present invention;

FIG. 2 is a perspective view of the support member and rigid contact structure incorporated in the trimmer potentiometer shown in FIG. 1;

FIG. 3 is a perspective view of the cover for the potentiometer support member;

FIG. 4 is a rear elevation of an assembled potentiometer having a four-sided housing; and

FIG. 5 is a rear elevation of an assembled potentiometer with a three-sided housing.

Referring now to FIG. 1, there is shown a trimmer potentiometer having a support member 10 comprising a central portion 11 and up-standing end portions 12 and 13. Bearings 14 and 15 mounted in the end portions 12 and 13 respectively, rotatably support a helically threaded adjustment shaft 16. A movable contact block 17 is engaged by the adjustment shaft and is adapted to be translated along the central portion 11 of the body between the end portions 12 and 13 upon rotation of shaft 16.

An elongated resistance element 20 and an elongated electrical conducting element (not shown) are mounted side by side on the central portion 11 of the support member 10. Support member 10 is preferably molded or cast from a single piece of electrical insulating material, a ceramic such as steatite being a highly suitable material. The resistance element 20 may be a wire wound resistor, a molded resistor, a deposited layer resistor, or any other suitable type. A deposited layer type of resistance element which is fired on a ceramic base is especially well adapted for use in the embodiment shown. Preferred deposited layer resistance elements comprise cermet resistance elements constructed according to the teachings of US. Patent No. 2,950,995 entitled Electrical Resistance Element and No. 2,950,996 entitled Electrical Resistance Material and Method of Making Same, a co-patentee of each being the inventor of the present invention. These patents are assigned to Beckman Instruments, Inc. Similarly, the electrical conducting elements may take various known forms, a film of silver fired on ceramic being preferred.

Electrical contact means 25 are carried on the contact block 17 for electrically connecting a point on the resistance element 21 with the conducting element.

The foregoing described structure, including additional specific details thereof is described and claimed in the co-pending application of James F. Gordon entitled Potentiometer and Method of Manufacturing Same, supra.

Referring now to FIG. 2, the potentiometer support member is molded with longitudinal grooves 30, 31 and 32. Each of these grooves terminate at the end 33 of the support member and at respective holes 34, 35 and 36 which extend completely through the central portion of the support member to the opposite side as shown in FIG. 1. Openings 35 and 36 are adjacent the respective ends of the resistance element and opening 34 is adjacent the conductive strip (not shown).

A rigid terminal structure is afforded by respective single strand bare conductors 37, 38 and 39 respectively accommodated in the grooves 30, 31 and 32 and the holes 34, 35 and 36. These conductors are preferably drawn from an oxide resistant alloy made readily solderable by a flash nickel plate followed by a gold plate. In the embodiment shown, each of these conductors is provided with an integral broad flat head abutting the top surface of the support member, e.g., conductors 38 and 39 are provided with respective heads 40, 41 as shown in FIG. 1. These heads are shown located adjacent to or abutting the resistance element 20.

Alternatively, the heads 40, 41 and like-head (not shown) of the conductor 37 are countersunk in recesses formed in the top surface of central portion 11 of the support member 10. In still another modification, the heads may be deleted and contact made with respective ends of the conductors 37, 38 and 39 located substantially flush with the surface of body portion 11.

Slightly different construction techniques will be required to assemble potentiometers using headed conductors than those without. In the former, the end opposite the head will be first passed through its respective hole from the top surface of the body portion 11. The conductor must then be bent to lie in its respective channel or groove 30, 31 or 32 and finally, the hooks shown may be formed at the conductor ends. In those potentiometers not utilizing a headed conductor, the conductors, if desired, may be preformed to fit the grooves 30, 31 and 32 and with end hooks as shown. Their opposite ends are then passed through respective holes in the body portion 11 from the underside thereof.

The specific form employed for the ends of the conductors connected to the resistance and conductor elements will be determined in part by the ease with which electrical connection may be made to these elements. Thus, if the resistance and conductor elements are applied by a silk screening procedure, it may be advantageous to use a countersunk or flush head. With other types of elements, such as a resistance wire supported upon a mandrel, the electrical connection may be facilitated by allowing a headed portion to protrude above the body portion 11. Also, it may be undesirable in some instances to use a head raised above the surface of the resistance element since the movable contact will then make and break with the resistance element when it is translated to extreme ends of the potentiometer. This action may cause arcing with high resistivity resistance elements.

In a preferred embodiment of this invention, the cermet resistance layer constructed in accordance with the aforementioned U.S. Patents 2,950,955 and 2,950,996 is applied directly over the terminating heads (whether protruding or flush) thereby insuring a low resistance contact to the resistance element and obviating an electrical make and break. In a like manner, the conductive layer may be applied directly over the terminating head (not shown) integral wtih the conductor 37. In order to insure a firm electrical contact between the resistance element and the terminating heads, the temperature coeflicient of expansion of the single strand conductor material should be similar to that of the resistance material so that exposure to high temperatures in either the firing cycle or in subsequent high ambient temperature environments will not serve to separate the heads 40,

41 from the resistance element 20. A representative material having the desired ccefiicient of expansion is an alloy comprising 29% nickel, 17% cobalt, 3% manganese, and the balance iron and sold under the trademark Kovar by the Stupakoff Ceramics and Manufacturing Company.

Each of the single strand conductors 37, 38 and 39 is preferably bonded to the support member 10 by melting a glass bead 43 (FIG. '1) in the respective holes 34, 35 and 36 These holes are preferably countersunk from the groove, as shown, to provide a cup-shaped receptacle for retaining the glass bead. The conductors are thus sealed to the frame thereby relieving any stress upon the flat head members formed at the ends fo the conductors. Accordingly, any mechanical forces applied to the ends of the conductors 37, 38 and 39 will not afifect the position of the head thereby insuring their permanent connection to the resistance element and conductive strip.

The bottom face of the support member it) is preferably covered by a cover member 46 shown in FIG. 3. This member is preferably constructed of the same material as the support member ltl and may be attached thereto by firing a low fusing glass frit or by employing a high temperature adhesive such as filled epoxy resin.

The assembly of the potentiometer is completed by a suitable housing positioned to enclose the internal components. As shown in FIG. 4, such a housing may comprise a four-sided housing 47 formed preferentially from a corrosion resistance metal such as a stainless steel and lined with an insulating material 48. Optionally, a threesided housing 49 shown in FIG. 5 may be employed. Each of these housings may be retained in a predetermined position with respect to the support member 10 by means of hollow rivets 50 passing through the housing and the potentiometer support member.

The foregoing described terminal structure provides a rigid terminal structure by means of relatively large single strand bare conductors while maintaining a very high leakage resistance and high voltage breakdown resistance. These desirable electrical characteristics are afforded by the substantial spacing of the contacts permitted by the structure described above. Thus, the grooves 30, 31 and 32 are spaced a substantial distance apart from each other and also from the components of the potentiometer which are mounted upon the opposite surface of the support member. The mechanical problems normally encountered with a solid conductor terminal are avoided by the seal formed in the countersunk bore as described above.

Although exemplary embodiments of the invention have been disclosed and discussed, it will be understood that other applications of the invention are possible and that the embodiments disclosed may be subjected to various changes, modifications and substitutions without necessarily departing from the spirit of the invention.

I claim:

1. A resistance element having rigid terminals extending from the rear of its housing comprising:

a long narrow substantially rectangular support member of electrically nonconductive material having a plurality of adjacent substantially parallel longitudinal grooves in the bottom face thereof each extending from one end of the support member to a respective opening extending upwardly through said support member, each of said openings comprising a countersunk bore connected to a smaller hole opening on the upper face of said member;

a resistance element mounted by said upper face of the support member;

a plurality of rigid terminal structures each comprising an uninsulated strand conductor having a broad flat head formed integral with one end thereof, each of said conductors being retained within a respective one of said grooves and its associated opening with said fiat head in electrical contact with said resistance element and the length of each of said strand conductors being at least coextensive with the length of said respective groove and the opening with which the respective strand conductor is associated;

means within said countersunk bore for sealing each of said conductors to said support member;

and a cover member of electrically nonconductive material attached to the bottom face of said support member and at least coextensive with said grooves thereby to enclose said strand conductors to reduce electrical current leakage therefrom within the confines of said element.

2. A resistance element having rigid terminals extending from the rear of its housing comprising:

a long narrow substantially rectangular support member of electrically nonconductive material having a plurality of adjacent substantially parallel longitudinal grooves in the bottom face thereof each extending from one end of the support member to a respective opening extending upwardly through said support member, each of said openings comprising a countersunk bore connected to a smaller hole opening on the upper face of said member;

a resistance element mounted by said upper face of said support member;

a plurality of rigid terminal structures each comprising an uninsulated strand conductor retained within a respective one of said grooves and its associated opening and having one end thereof in electrical contact with said resistance element and With the length of each of said strand conductors being at least coextensive with the length of said respective groove and the opening with which the respective strand conductor is associated;

means within said countersunk bore for sealing each of said conductors to said support member;

and a cover member of electrically nonconductive material attached to the bottom face of said support member and at least coextensive with said grooves thereby to enclose said strand conductors to reduce electrical current leakage therefrom Within the con fines of said element.

References Cited by the Examiner UNITED STATES PATENTS 599,352 2/1898 ONeilletal 33s-312 2,141,907 12/1938 Hathorn 338-184 2,606,985 8/1952 De Bell 338-311 X 2,674,677 4/1954 Anderson et al. 338- 307 X 2,713,625 7/11955 Johnson et 1 338-312 X 2,860,217 11/1958 Bourns 338180 2,873,336 2/1959 Tassara 338-174X 2,950,995 8/1960 Place et a1. 338-308 2,997,679 8/1961 Barden et a1 33s 180 3,096,500 7/1963 Daily et a1. 338-183 FOREIGN PATENTS 63,137 3/1955 France.

30 RICHARD M. WOOD, Primary Examiner.

ANTHONY BARTIS, Examiner. 

1. A RESISTANCE ELEMENT HAVING RIGID TERMINALS EXTENDING FROM THE REAR OF ITS HOUSING COMPRISING: A LONG NARROW SUBSTANTIALLY RECTANGULAR SUPPORT MEMBER OF ELECTRICALLY NONCONDUCTIVE MATERIAL HAVING A PLURALITY OF ADJACENT SUBSTANTIALLY PARALLEL LONGITUDINAL GROOVES IN THE BOTTOM FACE THEREOF EACH EXTENDING FROM ONE END OF THE SUPPORT MEMBER TO A RESPECTIVE OPENING EXTENDING UPWARDLY THROUGH SAID SUPPORT MEMBER, EACH OF SAID OPENINGS COMPRISING A COUNTERSUNK BORE CONNECTED TO A SMALLER HOLE OPENING ON THE UPPER FACE OF SAID MEMBER A RESISTANCE ELEMENT MOUNTED BY SAID UPPER FACE OF THE SUPPORT MEMBER; A PLURALITY OF RIGID TERMINAL STRUCTURES EACH COMPRISING AN UNINSULATED STRAND CONDUCTOR HAVING A BOARD FLAT HEAD FORMED INTEGRAL WITH ONE END THEREOF, EACH OF SAID CONDUCTORS BEING RETAINED WITHIN A RESPECTIVE ONE OF SAID GROOVES AND ITS ASSOCIATED OPENING WITH SAID FLAT HEAD IN ELECTRICAL CONTACT WITH SAID RESISTANCE ELEMENT AND WITH THE LENGTH OF EACH OF SAID STRAND CONDUCTORS BEING AT LEAST COEXTENSIVE WITH THE LENGTH OF SAID RESPECTIVE GROOVE AND THE OPENING WITH WHICH THE RESPECTIVE STRAND CONDUCTOR IS ASSOCIATED; MEANS WITHIN SAID COUNTERSUNK BORE FOR SEALING EACH OF SAID CONDUCTORS TO SAID SUPPORT MEMBER; AND A COVER MEMBER OF ELECTRICALLY NONCONDUCTIVE MATERIAL ATTACHED TO THE BOTTOM FACE OF SAID SUPPORT MEMBER AND AT LEAST COEXTENSIVE WITH SAID GROOVES THEREBY TO ENCLOSE SAID STRAND CONDUCTORS TO REDUCE ELECTRICAL CURRENT LEAKAGE THEREFROM WITHIN THE CONFINES OF SAID ELEMENT. 